Medical staff in the the ward in Raigmore Hospital in Inverness have had to deal with several cases of diarrhoea and vomiting since Friday.
Since the onset of illness started on the ward nine patients have experienced symptoms.
A number of staff have also been affected, and they are recovering at home.
Testing has confirmed that two of the affected patients' symptoms are caused by norovirus.
The virus, which causes diarrhoea, nausea and vomiting, spreads in the air where someone has had diarrhoea or vomited, and is extremely difficult to contain.
Dr Jonty Mills, consultant microbiologist for NHS Highland, said: "As well as restricting visiting to the affected wards we are also asking people not to come to the hospitals to visit if they have had any vomiting or diarrhoea within the previous 48 hours.
"By doing this we will be able to limit the spread as much as possible.
"Hospital staff will of course be very happy to talk to visitors on the phone so they can get updates on how their relatives are."
There is no specific treatment for norovirus and sufferers outside the hospital should stay at home and drink plenty of water.